Typically, a hard bias film is positioned at an end of a free layer of a magnetic head, and is constructed to apply a hard bias magnetic field to the free layer. This hard bias magnetic field converts the magnetization of the free layer to a single magnetic domain, thereby suppressing noise. If the magnetization of the free layer is not converted to a single magnetic domain, but has a multitude of domains, noise is generated.
Conventionally, with increased recording density, the read gap, i.e., the vertical separation of the magnetic shield from the read sensor, is narrowed, with the consequence that the hard bias magnetic field is more readily absorbed by the magnetic shield, which causes the hard bias magnetic field to be decreased as a result of this absorption. As a result, noise such as Barkhausen noise is generated in the magnetic head, which is undesirable.
A portion of a magnetic head 500 is shown in FIG. 5 according to the prior art. A conventional magnetic head 500 comprises a magnetic shield 502, a protective layer 504 between the magnetic shield 502 and a hard bias film 514, and a sensor 512, such as a tunneling magnetoresistance (TMR) sensor. In some magnetic heads 500, an insulating layer 506, a first underlayer 508 and a second underlayer 510 may be positioned below the hard bias film 514. As shown, magnetization 513 of the hard bias film 514 (the hard bias magnetic field) and magnetization 503 of the magnetic shield 502 are parallel (e.g., they have the same direction). This results in the hard bias magnetic field tending to be absorbed by the magnetic shield 502, which also causes noise to occur.
Accordingly, it would be beneficial to have a magnetic head design which has a high recording density but which also reduces the amount of the hard bias magnetic field which is absorbed by the magnetic shield.